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Abstract

Increasing global temperatures have an impact on flowering, and the underlying mechanisms are just beginning to be unravelled1,2. Elevated temperatures can induce flowering, and different mechanisms that involve either activation or de-repression of FLOWERING LOCUS T (FT) by transcription factor PHYTOCHROME INTERACTING FACTOR 4 (PIF4) or the FLOWERING LOCUS M (FLM)–SHORT VEGETATIVE PHASE (SVP) complex, respectively, have been suggested to be involved3,​4,​5,​6. Thermosensitivity in flowering has been mapped to FLM5, which encodes a floral repressor7,8. FLM undergoes alternative splicing8 and it has been suggested that temperature-dependent alternative splicing leads to differential accumulation of the FLM-β and FLM-δ transcripts, encoding proteins with antagonistic effects, and that their ratio determines floral transition4. Here we show that high temperatures downregulate FLM expression by alternative splicing coupled with nonsense-mediated mRNA decay (AS-NMD). We identify thermosensitive splice sites in FLM and show that the primary effect of temperature is explained by an increase in NMD target transcripts. We also show that flm is epistatic to pif4, which suggests that most of the PIF4 effects are FLM dependent. Our findings suggest a model in which the loss of the floral repressor FLM occurs through mRNA degradation in response to elevated temperatures, signifying a role for AS-NMD in conferring environmental responses in plants.

Acknowledgements

We thank C.A. Kraupner-Taylor for technical support, the Arabidopsis Biological Resource Centre (ABRC) and C. Fankhauser for seeds, H. Eimer and W. Zhu for providing some of the DNA and RNA samples used in this study, and J. Bowman, R. Burke, R. Clark, D. Smyth and W. Zhu for critical reading of the manuscript. This work is supported by Australian Research Council Discovery Projects DP110100964 and DP0987835 to S.S. and S.B., respectively, an ARC-Discovery Early Career Researcher Award (DE130100320) to C.T., an ARC Future Fellowship (FT100100377) to S.B. and funds from the Larkins Fellowship programme at Monash University to S.B.

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Contributions

S.S. and S.B. designed the study. S.S. carried out most of the experiments. S.S., C.D., A.S., C.T. and S.B. analysed the data. S.S., C.D. and S.B. wrote the manuscript with input from all authors. S.B. supervised the study.